This application relates to coated articles, and, more particularly, to a superalloy article having a metallic overlay protective coating.
In an aircraft gas turbine (jet) engine, air is drawn into the front of the engine, compressed by a shaft-mounted compressor, and mixed with fuel. The mixture is burned, and the hot exhaust gases are passed through a turbine mounted on the same shaft. The flow of combustion gas turns the turbine, which turns the shaft and provides power to the compressor. The hot exhaust gases flow from the back of the engine driving it and the aircraft forwardly.
The hotter the combustion and exhaust gases, the more efficient is the operation of the jet engine. There is thus an incentive to raise the combustion and exhaust gas temperatures. However, the maximum temperature of the combustion gases is normally limited by the materials used to fabricate the turbine vanes and turbine blades of the turbine. In current engines, the turbine vanes and blades are made of nickel-based superalloys, and can operate at temperatures of up to 1900-2100.degree. F.
Many approaches have been used to increase the operating temperature limit of the turbine blades and vanes to their current levels. The composition and processing of the materials themselves have been improved, and physical cooling techniques are employed.
In another approach, a protective layer or a ceramic/metal thermal barrier coating (TBC) system is applied to the turbine blade or turbine vane component, which acts as a substrate. The protective layer with no overlying ceramic layer (in which case the protective layer is termed an "environmental coating") is useful in intermediate-temperature applications. The currently known protective layers include diffusion aluminides and MCrAlY(X) overlays.
A ceramic thermal barrier coating layer may be applied overlying the protective layer, to form a thermal barrier coating system (in which case the protective layer is termed a "bond coat"). The thermal barrier coating system is useful in higher-temperature applications. The ceramic thermal barrier coating, insulates the component from the combustion gas, permitting the combustion gas to be hotter than would otherwise be possible with the particular material and fabrication process of the substrate.
Although these coating systems are operable, there is always the need to achieve further improvements in maximum operating temperatures and times of coated articles. The present invention fulfills this need and further provides related advantages.